Publications
318 results found
Ciappina MF, Perez-Hernandez JA, Landsman AS, et al., 2017, Attosecond physics at the nanoscale, Publisher: IOP PUBLISHING LTD
- Author Web Link
- Open Access Link
- Cite
- Citations: 246
Mercer IP, Witting T, Driver T, et al., 2017, Angle-resolved coherent wave mixing using a 4 fs ultra-broad bandwidth laser, Optics Letters, Vol: 42, Pages: 859-862, ISSN: 0146-9592
We demonstrate angle-resolved coherent (ARC) wave mixing using 4 fs light pulses derived from a laser source that spans 550–1000 nm. We believe this to be the shortest pulse duration used to date in coherent multi-dimensional spectroscopy. The marriage of this ultra-broad band, few-cycle coherent source with the ARC technique will permit new investigations of the interplay between energy transfers and quantum superposition states spanning 8200 cm−1. We applied this configuration to measurements on the photosynthetic low light (LL) complex from Rhodopseudomonas palustris in solution at ambient temperature. We observe bi-exponential population dynamics for energy transfer across 5500 cm−1 (0.65 eV), which we attribute to energy transfer from the transition of bacteriochlorophylls to the B850 pigment of the complex. We believe for the first time, to the best of our knowledge, we demonstrate that ARC maps can be recorded using a single laser pulse.
Schuette B, Ye P, Patchkovskii S, et al., 2016, Strong-field ionization of clusters using two-cycle pulses at 1.8 μm, Scientific Reports, Vol: 6, ISSN: 2045-2322
The interaction of intense laser pulses with nanoscale particles leads to the production of high-energy electrons, ions, neutral atoms, neutrons and photons. Up to now, investigations have focused on near-infrared to X-ray laser pulses consisting of many optical cycles. Here we study strong-field ionization of rare-gas clusters (103 to 105 atoms) using two-cycle 1.8 μm laser pulses to access a new interaction regime in the limit where the electron dynamics are dominated by the laser field and the cluster atoms do not have time to move significantly. The emission of fast electrons with kinetic energies exceeding 3 keV is observed using laser pulses with a wavelength of 1.8 μm and an intensity of 1 × 1015 W/cm2, whereas only electrons below 500 eV are observed at 800 nm using a similar intensity and pulse duration. Fast electrons are preferentially emitted along the laser polarization direction, showing that they are driven out from the cluster by the laser field. In addition to direct electron emission, an electron rescattering plateau is observed. Scaling to even longer wavelengths is expected to result in a highly directional current of energetic electrons on a few-femtosecond timescale.
Decleva P, Orr-Ewing AJ, Kowalewski M, et al., 2016, Structural dynamics: general discussion, FARADAY DISCUSSIONS, Vol: 194, Pages: 583-620, ISSN: 1359-6640
Austin DR, McGrath F, Miseikis L, et al., 2016, Role of tunnel ionization in high harmonic generation from substituted benzenes., Faraday Discussions, Vol: 194, Pages: 349-368, ISSN: 1364-5498
We theoretically study high-harmonic generation in toluene, ortho-xylene and fluorobenzene driven by a 1.8 μm ultrashort pulse. We find that the chemical substitutions have a strong influence on the amplitude and phase of the emission from the highest occupied molecular orbital, despite having a small influence on the orbital itself. We show that this influence is due to the tunnel ionization step, which depends critically on the sign and amplitude of the asymptotic part of the wave function. We discuss how these effects would manifest in phase-sensitive high-harmonic generation spectroscopy experiments.
Milne CJ, Weber PM, Kowalewski M, et al., 2016, Attosecond processes and X-ray spectroscopy: general discussion, Faraday Discussions, Vol: 194, Pages: 427-462, ISSN: 1359-6640
Orr-Ewing AJ, Verlet JRR, Penfold TJ, et al., 2016, Electronic and non-adiabatic dynamics: general discussion, Faraday Discussions, Vol: 194, Pages: 209-257, ISSN: 1359-6640
Johnson AS, Miseikis L, Wood DA, et al., 2016, Measurement of sulfur L2,3 and carbon K edge XANES in a polythiophene film using a high harmonic supercontinuum, Structural Dynamics, Vol: 3, ISSN: 2329-7778
We use a high harmonic generated supercontinuum in the soft X-ray region to measure X-ray absorption near edge structure (XANES) spectra in polythiophene (poly(3-hexylthiophene)) films at multiple absorption edges. A few-cycle carrier-envelope phase-stable laser pulse centered at 1800 nm was used to generate a stable soft X-ray supercontinuum, with amplitude gating limiting the generated pulse duration to a single optical half-cycle. We report a quantitative transmission measurement of the sulfur L2,3 edge over the range 160-200 eV and the carbon K edge from 280 to 330 eV. These spectra show all the features previously reported in the XANES spectra of polythiophene, but for the first time they are measured with a source that has an approximately 1 fs pulse duration. This study opens the door to measurements that can fully time-resolve the photoexcited electronic dynamics in these systems.
Austin DR, witting T, sebastien J, et al., 2016, Spatio-temporal characterization of intense few-cycle 2 μm pulses, Optics Express, Vol: 24, Pages: 24786-24798, ISSN: 1094-4087
We present a variant of spatially encoded spectral shearing interferometry for measuring two-dimensional spatio-temporal slices of few-cycle pulses centered around 2μm. We demonstrate experimentally that the device accurately retrieves the pulse-front tilt caused by angular dispersion of two-cycle pulses. We then use the technique to characterize 500–650 μJ pulses from a hollow fiber pulse compressor, with durations as short as 7.1 fs (1.3 optical cycles).
Witting T, Greening D, Walke D, et al., 2016, Time-domain ptychography of over-octave-spanning laser pulses in the single-cycle regime., Optics Letters, Vol: 41, Pages: 4218-4221, ISSN: 1539-4794
We report, to the best of our knowledge, the first application of time-domain ptychography for the characterization of few-cycle laser pulses. Our method enables zero-additional phase measurements of over-octave-spanning laser pulses in the single cycle regime. The spectral phase is recovered using a robust ptychography algorithm that requires no input apart from the measured data trace. In addition to numerical tests, we validate our new device experimentally by reconstructing the complex electric field of a 1.5 cycle laser pulse with a bandwidth spanning 490 to 1060 nm. We further check the accuracy of our device by comparing the measured phases of octave-spanning chirped pulses to the known dispersion of fused silica glass.
Simpson ER, Sanchez-Gonzalez A, Austin DR, et al., 2016, Polarisation response of delay dependent absorption modulation in strong field dressed helium atoms probed near threshold, New Journal of Physics, Vol: 18, ISSN: 1367-2630
Wepresent the first measurement of the vectorial response of strongly dressed helium atoms probed by an attosecond pulse train (APT) polarised either parallel or perpendicular to the dressing field polarisation. The transient absorption is probed as a function of delay between the APT and the Linearly polarised 800 nmfield of peak intensity 1.3∗1014 W cm-2. The APT spans the photon energy range 1642 eV, covering the first ionisation energy of helium (24.59 eV). With parallel polarised dressing and probing fields, we observe modulations with periods of one half and one quarter of the dressing field period. When the polarisation of the dressing field is altered from parallel to perpendicular with respect to the APT polarisation we observe a large suppression in the Modulation depth of the above ionisation threshold absorption. In addition to this we present the intensity dependence of the harmonic modulation depth as a function of delay between the dressing and probe fields, with dressing field peak intensities ranging from 2∗1012 to 2∗1014 W cm-2.We compare our experimental results with a full-dimensional solution of the single-atom time-dependent (TD) Schrdinger equation obtained using the recently developed abinitio TDB-spline ADCmethod and find good qualitative agreement for the above threshold harmonics.
Schütte B, Golubev N, Kuleff AI, et al., 2016, Slow electrons from intense laser-cluster interactions
A surprisingly dominant contribution of slow electrons is observed following NIR strong-field ionization of clusters. This is consistent with highly efficient intra-Rydberg correlated electronic decay processes, from which the emission of low-energy electrons is expected.
Marangos JP, 2016, Development of high harmonic generation spectroscopy of organic molecules and biomolecules, Journal of Physics B - Atomic Molecular and Optical Physics, Vol: 49, ISSN: 0953-4075
In this review we will discuss the topic of high order harmonic generation (HHG) from samples of organic and bio-molecules. The possibility to extract useful dynamical and structural information from the measurement of the HHG emission, a technique termed high harmonic generation spectroscopy (HHGS), will be the special focus of our discussions. We will begin by introducing the salient facts of HHG from atoms and simple molecules and explaining the principles behind HHGS. Next the technical difficulties associated with HHG from samples of organic molecules and biomolecules, principally the low sample density and the low ionization potential, will be examined. Then we will present some recent experiments where HHG spectra from samples of these molecules have been measured and discuss what has been learned from these measurements. Finally we will look at the future prospects for HHG spectroscopy of organic molecules, discussing some of the technical and in principle limits of the technique and methods that may ameliorate these limits.
Witting T, Austin DR, Barillot T, et al., 2016, Self-referenced characterization of space-time couplings in near-single-cycle laser pulses, Optics Letters, Vol: 41, Pages: 2382-2385, ISSN: 1539-4794
We report on the characterization of space–time couplingsin high-energy sub-2-cycle 770 nm laser pulses using a selfreferencingsingle-frame method. Using spatially encodedarrangement filter-based spectral phase interferometry fordirect electric field reconstruction, we characterize fewcyclepulses with a wavefront rotation of 2.8 × 1011 rev∕s(1.38 mrad per half-cycle) and pulses with pulse fronttilts ranging from −0.33 fs∕μm to −3.03 fs∕μm in thefocus.
Wyatt AS, Witting T, Schiavi A, et al., 2016, Attosecond sampling of arbitrary optical waveforms, Optica, Vol: 3, Pages: 303-310, ISSN: 2334-2536
Advances in the generation of ultrashort laser pulses, and the emergence of new research areas such as attosecond science, nanoplasmonics, coherent control, and multidimensional spectroscopy, have led to the need for a new class of ultrafast metrology that can measure the electric field of complex optical waveforms spanning the ultraviolet to the infrared. Important examples of such waveforms are those produced by spectral control of ultrabroad bandwidth pulses, or by Fourier synthesis. These are typically tailored for specific purposes, such as to increase the photon energy and flux of high-harmonic radiation, or to control dynamical processes by steering electron dynamics on subcycle time scales. These applications demand a knowledge of the full temporal evolution of the field. Conventional pulse measurement techniques that provide estimates of the relative temporal or spectral phase are unsuited to measure such waveforms. Here we experimentally demonstrate a new, all-optical method for directly measuring the electric field of arbitrary ultrafast optical waveforms. Our method is based on high-harmonic generation (HHG) driven by a field that is the collinear superposition of the waveform to be measured with a stronger probe laser pulse. As the delay between the pulses is varied, we show that the field of the unknown waveform is mapped to energy shifts in the high-harmonic spectrum, allowing a direct, accurate, and rapid retrieval of the electric field with subcycle temporal resolution at the location of the HHG.
Austin DR, Witting T, Ye P, et al., 2016, Temporal Characterization of Two Octave Hollow Fiber Supercontinuum
We measure the temporal profile of a 600 μJ hollow fiber supercontinuum spanning 640-2600 nm. At the fiber output, we observe extreme self-steepening and self-compression. The pulse is suitable for multi-channel compression to the sub-cycle regime.
Fukuzawa H, Tachibana T, Motomura K, et al., 2016, Electron spectroscopy of rare-gas clusters irradiated by x-ray free-electron laser pulses from SACLA, JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 49, ISSN: 0953-4075
- Author Web Link
- Cite
- Citations: 9
Sanchez-Gonzalez A, Barillot TR, Squibb RJ, et al., 2015, Auger electron and photoabsorption spectra of glycine in the vicinity of the oxygen K-edge measured with an X-FEL, JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 48, ISSN: 0953-4075
- Author Web Link
- Cite
- Citations: 9
Liekhus-Schmaltz CE, Tenney I, Osipov T, et al., 2015, Ultrafast isomerization initiated by X-ray core ionization, Nature Communications, Vol: 6, ISSN: 2041-1723
Rapid proton migration is a key process in hydrocarbon photochemistry. Charge migration and subsequent proton motion can mitigate radiation damage when heavier atoms absorb X-rays. If rapid enough, this can improve the fidelity of diffract-before-destroy measurements of biomolecular structure at X-ray-free electron lasers. Here we study X-ray-initiated isomerization of acetylene, a model for proton dynamics in hydrocarbons. Our time-resolved measurements capture the transient motion of protons following X-ray ionization of carbon K-shell electrons. We Coulomb-explode the molecule with a second precisely delayed X-ray pulse and then record all the fragment momenta. These snapshots at different delays are combined into a ‘molecular movie’ of the evolving molecule, which shows substantial proton redistribution within the first 12 fs. We conclude that significant proton motion occurs on a timescale comparable to the Auger relaxation that refills the K-shell vacancy.
Das T, Augstein BB, Faria CFDM, et al., 2015, Extracting an electron's angle of return from shifted interference patterns in macroscopic high-order-harmonic spectra of diatomic molecules, PHYSICAL REVIEW A, Vol: 92, ISSN: 1050-2947
- Author Web Link
- Cite
- Citations: 4
McGrath FC, 2015, Extending High Harmonic Generation Spectroscopy to New Molecular Species
Tachibana T, Jurek Z, Fukuzawa H, et al., 2015, Nanoplasma formation by high intensity hard x-rays, Scientific Reports, Vol: 5, ISSN: 2045-2322
Using electron spectroscopy, we have investigated nanoplasma formation from noble gas clusters exposed to high-intensity hard-x-ray pulses at ~5 keV. Our experiment was carried out at the SPring-8 Angstrom Compact free electron LAser (SACLA) facility in Japan. Dedicated theoretical simulations were performed with the molecular dynamics tool XMDYN. We found that in this unprecedented wavelength regime nanoplasma formation is a highly indirect process. In the argon clusters investigated, nanoplasma is mainly formed through secondary electron cascading initiated by slow Auger electrons. Energy is distributed within the sample entirely through Auger processes and secondary electron cascading following photoabsorption, as in the hard x-ray regime there is no direct energy transfer from the field to the plasma. This plasma formation mechanism is specific to the hard-x-ray regime and may, thus, also be important for XFEL-based molecular imaging studies. In xenon clusters, photo- and Auger electrons contribute more significantly to the nanoplasma formation. Good agreement between experiment and simulations validates our modelling approach. This has wide-ranging implications for our ability to quantitatively predict the behavior of complex molecular systems irradiated by high-intensity hard x-rays.
Fabris D, Witting T, Okell WA, et al., 2015, Synchronized pulses generated at 20 eV and 90 eV for attosecond pump-probe experiments, Nature Photonics, Vol: 9, Pages: 383-387, ISSN: 1749-4885
The development of attosecond pulses across different photon energies is an essential precursor to performing pump–probe attosecond experiments in complex systems, where the potential of attosecond science1 can be further developed2,3. We report the generation and characterization of synchronized extreme ultraviolet (90 eV) and vacuum ultraviolet (20 eV) pulses, generated simultaneously via high-harmonic generation. The vacuum ultraviolet pulses are well suited for pump–probe experiments that exploit the high photo-ionization cross-sections of many molecules in this spectral region4 as well as the higher photon flux due to the higher conversion efficiency of the high harmonic generation process at these energies5. We temporally characterized all pulses using the attosecond streaking technique6 and the FROG-CRAB retrieval method7. We report 576 ± 16 as pulses at 20 eV and 257 ± 21 as pulses at 90 eV. Our demonstration of synchronized attosecond pulses at different photon energies, which are inherently jitter-free due to the common-path geometry implemented, offers unprecedented possibilities for pump–probe studies.
Okell WA, Witting T, Fabris D, et al., 2015, Temporal broadening of attosecond photoelectron wavepackets from solid surfaces, Optica, Vol: 2, Pages: 383-387, ISSN: 2334-2536
Wyatt AS, Matía-Hernando P, Johnson AS, et al., 2015, Compression and amplification of SWIR single-cycle pulses for water window attosecond pulse generation
- Cite
- Citations: 1
Simpson ER, Sanchez-Gonzalez A, Siegel T, et al., 2015, A beamline for attosecond pump-probe experiments: Towards tracking ultrafast electron dynamics in atoms and molecules, Conference on Ultrafast Nonlinear Imaging and Spectroscopy III, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
Marangos JP, 2015, A light year: Journal of Modern Optics celebrates the International Year of Light, JOURNAL OF MODERN OPTICS, Vol: 62, Pages: 413-414, ISSN: 0950-0340
Haessler S, Balciunas T, Fan G, et al., 2015, Optimization of Quantum Trajectories Driven by Strong-Field Waveforms, 19th International Conference on Ultrafast Phenomena, Publisher: SPRINGER-VERLAG BERLIN, Pages: 72-77, ISSN: 0930-8989
- Author Web Link
- Cite
- Citations: 2
Cooper B, Kolorenc P, Frasinski LJ, et al., 2014, Analysis of a measurement scheme for ultrafast hole dynamics by few femtosecond resolution X-ray pump-probe Auger spectroscopy, Faraday Discussions, Vol: 171, Pages: 93-111, ISSN: 1364-5498
Ultrafast hole dynamics created in molecular systems as a result of sudden ionisation is the focus of much attention in the field of attosecond science. Using the molecule glycine we show through ab initio simulations that the dynamics of a hole, arising from ionisation in the inner valence region, evolves with a timescale appropriate to be measured using X-ray pulses from the current generation of SASE free electron lasers. The examined pump–probe scheme uses X-rays with photon energy below the K edge of carbon (275–280 eV) that will ionise from the inner valence region. A second probe X-ray at the same energy can excite an electron from the core to fill the vacancy in the inner-valence region. The dynamics of the inner valence hole can be tracked by measuring the Auger electrons produced by the subsequent refilling of the core hole as a function of pump–probe delay. We consider the feasibility of the experiment and include numerical simulation to support this analysis. We discuss the potential for all X-ray pump-X-ray probe Auger spectroscopy measurements for tracking hole migration.
Arrell CA, Ojeda J, Sabbar M, et al., 2014, A simple electron time-of-flight spectrometer for ultrafast vacuum ultraviolet photoelectron spectroscopy of liquid solutions, Review of Scientific Instruments, Vol: 85, ISSN: 1089-7623
We present a simple electron time of flight spectrometer for time resolved photoelectron spectroscopy of liquid samples using a vacuum ultraviolet (VUV) source produced by high-harmonic generation. The field free spectrometer coupled with the time-preserving monochromator for the VUV at the Artemis facility of the Rutherford Appleton Laboratory achieves an energy resolution of 0.65 eV at 40 eV with a sub 100 fs temporal resolution. A key feature of the design is a differentially pumped drift tube allowing a microliquid jet to be aligned and started at ambient atmosphere while preserving a pressure of 10−1 mbar at the micro channel plate detector. The pumping requirements for photoelectron (PE) spectroscopy in vacuum are presented, while the instrument performance is demonstrated with PE spectra of salt solutions in water. The capability of the instrument for time resolved measurements is demonstrated by observing the ultrafast (50 fs) vibrational excitation of water leading to temporary proton transfer.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.